(276033) 2002 AJ129, provisional designation 2002 AJ129, is a Mercury-crossing asteroid. It has the ninth-smallest perihelion of all numbered asteroids, after asteroids such as 2000 BD19, 2004 UL, and 2008 XM.[6] It makes close approaches to all of the inner planets[3] and asteroid 4 Vesta,[7] the asteroid is estimated to be between 0.5–1.2 kilometers (0.3–0.7 mi) across.[5] In January 2018 there was a lot of media hype about this asteroid being classified as a potentially hazardous asteroid even though there is no known threat of an impact for hundreds if not thousands of years, the media has compared the size of the asteroid to the Burj Khalifa in Dubai.[8]

On 4 February 2018 at 21:31 UT, the asteroid passed about 0.028126 AU (4,207,600 km; 2,614,500 mi) from Earth.[3][10] The 2018 Earth approach distance was known with a 3-sigma accuracy of ±200 km.[3]Goldstone is scheduled to observe the asteroid from 3–6 February.[11] By 4 February 2018 11:00 UT, the asteroid brightened to apparent magnitude 14 and had a solar elongation of more than 100°.[12]

On 8 February 2172, the asteroid will pass about 0.00458 AU (685,000 km; 426,000 mi) from Earth.[3] The 2172 Earth approach distance is known with a 3-sigma accuracy of ±4000 km.

As we look even further into the future the known trajectory becomes more divergent. By the Earth approach of 0.24 AU (36,000,000 km; 22,000,000 mi) on 19 February 2196 the uncertainty increases to ±2.4 million km.[3]

1.
Near-Earth Asteroid Tracking
–
Near-Earth Asteroid Tracking was a program run by NASA and the Jet Propulsion Laboratory, surveying the sky for near-Earth objects. NEAT was conducted from December 1995 until April 2007, at GEODSS on Hawaii, with the discovery of more than 40 thousand minor planets, NEAT has been one of the most successful programs in this field, comparable to the Catalina Sky Survey, LONEOS and Mount Lemmon Survey. NEAT was the successor of the Palomar Planet-Crossing Asteroid Survey, the original principal investigator was Eleanor F. Helin, with co-investigators Steven H. Pravdo and David L. Rabinowitz. NEAT has an agreement with the U. S. Air Force to use a GEODSS telescope located on Haleakala, Maui. GEODSS stands for Ground-based Electro-Optical Deep Space Surveillance and these wide field Air Force telescopes were designed to optically observe Earth orbital spacecraft, the NEAT team designed a CCD camera and computer system for the GEODSS telescope. The CCD camera format is 4096 ×4096 pixels and the field of view is 1. 2° ×1. 6°, beginning in April 2001, the Samuel Oschin telescope was also put into service to discover and track near-Earth objects. This telescope is equipped with a camera containing 112 CCDs each 2400 ×600 and this is the telescope that produced the images leading to the discovery of 50000 Quaoar in 2002, and 90377 Sedna in 2003 and the dwarf planet Eris. In addition to discovering thousands of asteroids, NEAT is also credited with the co-discovery of periodic comet 54P/de Vico-Swift-NEAT, the C/2001 Q4 comet was discovered on August 24,2001 by NEAT. An asteroid was named in its honour,64070 NEAT, in early 2005,1996 PW was discovered on 1996 August 9 by a NEAT automated search camera on Haleakalā, Hawaii. It was the first object that was not a comet discovered on an orbit typical of a long-period comets. This is raised the possibility it was a comet or a usual asteroid. List of Near-Earth asteroids by distance from Sun Minor Planet Center Planetary Data System Spaceguard Near Earth Asteroid Tracking

2.
Haleakala Observatory
–
The Haleakalā Observatory on the island of Maui, also known as the Haleakalā High Altitude Observatory Site, is the location of Hawaiis first astronomical research observatory. It is owned by the Institute for Astronomy of the University of Hawaii, tenants include the Air Force Research Laboratory and the Las Cumbres Observatory Global Telescope Network. At over 3,050 meters in altitude, the summit of Haleakalā is above one third of the Earths atmosphere and has excellent astronomical seeing conditions, the Mees Solar Observatory is named after Kenneth Mees and dedicated in 1964. It consists of one dome with multiple instruments sharing a common mount, currently, the 1.8 m PS1 prototype telescope is in operation and the PS2 is under construction. The Faulkes Telescope North, part of the Faulkes Telescope Project, is a 2.0 m reflecting telescope owned and operated by the Las Cumbres Observatory Global Telescope Network and it provides remote access to a research-quality telescope primarily to students in the United Kingdom. The TLRS-4 Laser Ranging System is part of the International Laser Ranging Service, the TLRS-4 replaced an older facility in order to provide continuity of data. The old facility now houses telescopes of the Pan-STARRS project, the Zodiacal Light Observatory currently consists of two instruments. The Scatter-free Observatory for Limb Active Regions and Coronae telescope is a 0.5 m off-axis reflecting coronagraph that is used to study the Suns corona, the Day-Night Seeing Monitor Telescope System makes telescope-independent observations of perturbations in the atmosphere above Haleakala. The Air Force Office of Scientific Research of the Air Force Research Laboratory operates the Maui Space Surveillance Complex, located at the MSSC are the 3.67 m Advanced Electro Optical System Telescope, the Maui Space Surveillance System, and the Ground-based Electro-Optical Deep Space Surveillance. The MSSS uses a number of assets, including a 1.6 m telescope, two 1.2 m telescopes on a common mount, a 0.8 m beam director/tracker. The GEODSS uses two 1.0 m telescopes and one 0.38 m telescope, the Advanced Technology Solar Telescope is a 4.0 m solar telescope currently under construction by the National Solar Observatory. The AFRL has plans to build a mirror re-coating facility adjacent to the AEOS building, a Baker-Nunn telescope operated from 1957 to 1976 as part of Project Space Track. The Lunar Ranging Experiment Observatory operated from 1974 until 1994, the Pan-STARRS PS1 now resides in the south dome of the LURE facility and the PS2 is being built in the north dome. The University of Chicago Enrico Fermi Institute operated the Haleakala Cosmic Ray Neutron Monitor Station from 1991 to 2007, the Haleakala Gamma Ray Observatory was a six-mirror Imaging Atmospheric Cherenkov Telescope on an equatorial mount. It began operating in 1981 and was upgraded in 1988, the Multicolor Active Galactic Nuclei Monitoring was a 2.0 m near infrared telescope operated by the University of Tokyo. It was housed in the LURE facilitys north dome from 1998 to 2008, observations of airglow were made from a platform near the middle of the site in the 1960s and 1970s. The platform is now used for temporary projects, the Near-Earth Asteroid Tracking program operated from 2000 to 2007 using one of the MSSS1.2 m telescopes. The Federal Aviation Administration operates a facility immediately to the west of the observatory site, the Department of Energy also operates a facility immediately to the west of the observatory site

3.
Minor planet
–
A minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor exclusively classified as a comet. Minor planets can be dwarf planets, asteroids, trojans, centaurs, Kuiper belt objects, as of 2016, the orbits of 709,706 minor planets were archived at the Minor Planet Center,469,275 of which had received permanent numbers. The first minor planet to be discovered was Ceres in 1801, the term minor planet has been used since the 19th century to describe these objects. The term planetoid has also used, especially for larger objects such as those the International Astronomical Union has called dwarf planets since 2006. Historically, the asteroid, minor planet, and planetoid have been more or less synonymous. This terminology has become complicated by the discovery of numerous minor planets beyond the orbit of Jupiter. A Minor planet seen releasing gas may be classified as a comet. Before 2006, the IAU had officially used the term minor planet, during its 2006 meeting, the IAU reclassified minor planets and comets into dwarf planets and small Solar System bodies. Objects are called dwarf planets if their self-gravity is sufficient to achieve hydrostatic equilibrium, all other minor planets and comets are called small Solar System bodies. The IAU stated that the minor planet may still be used. However, for purposes of numbering and naming, the distinction between minor planet and comet is still used. Hundreds of thousands of planets have been discovered within the Solar System. The Minor Planet Center has documented over 167 million observations and 729,626 minor planets, of these,20,570 have official names. As of March 2017, the lowest-numbered unnamed minor planet is 1974 FV1, as of March 2017, the highest-numbered named minor planet is 458063 Gustavomuler. There are various broad minor-planet populations, Asteroids, traditionally, most have been bodies in the inner Solar System. Near-Earth asteroids, those whose orbits take them inside the orbit of Mars. Further subclassification of these, based on distance, is used, Apohele asteroids orbit inside of Earths perihelion distance. Aten asteroids, those that have semi-major axes of less than Earths, Apollo asteroids are those asteroids with a semimajor axis greater than Earths, while having a perihelion distance of 1.017 AU or less. Like Aten asteroids, Apollo asteroids are Earth-crossers, amor asteroids are those near-Earth asteroids that approach the orbit of Earth from beyond, but do not cross it

4.
Apollo asteroid
–
The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth crossing asteroids that have an orbital semi-major axis greater than that of the Earth, as of November 2016, the steadily growing number of known Apollo asteroids has reached a total of 8,180 members. It is by far the largest group of objects, compared to the Aten, Amor. Currently, there are 1,133 numbered Apollos, asteroids are not numbered until they have been observed at two or more oppositions. There are also 1,472 Apollo asteroids that are enough. The closer their semi-major axis is to Earths, the eccentricity is needed for the orbits to cross. The largest known Apollo asteroid is 1866 Sisyphus, with a diameter of about 8.5 km, examples of known Apollo asteroids include, Apollo asteroids Apollo asteroid records List of Apollo minor planets

5.
Near-Earth object
–
A near-Earth object is any small Solar System body whose orbit brings it into proximity with Earth. By definition, a solar system body is a NEO if its closest approach to the Sun is less than 1.3 astronomical unit and it is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. NEOs have become of increased interest since the 1980s because of increased awareness of the potential danger some of the asteroids or comets pose, and mitigations are being researched. In January 2016, NASA announced the Planetary Defense Coordination Office to track NEOs larger than 30 to 50 meters in diameter and coordinate an effective threat response, NEAs have orbits that lie partly between 0.983 and 1.3 AU away from the Sun. When a NEA is detected it is submitted to the IAUs Minor Planet Center for cataloging, some NEAs orbits intersect that of Earths so they pose a collision danger. The United States, European Union, and other nations are currently scanning for NEOs in an effort called Spaceguard. In the United States and since 1998, NASA has a mandate to catalogue all NEOs that are at least 1 kilometer wide. In 2006, it was estimated that 20% of the objects had not yet been found. In 2011, largely as a result of NEOWISE, it was estimated that 93% of the NEAs larger than 1 km had been found, as of 5 February 2017, there have been 875 NEAs larger than 1 km discovered, of which 157 are potentially hazardous. The inventory is much less complete for smaller objects, which still have potential for scale, though not global. Potentially hazardous objects are defined based on parameters that measure the objects potential to make threatening close approaches to the Earth. Mostly objects with an Earth minimum orbit intersection distance of 0.05 AU or less, objects that cannot approach closer to the Earth than 0.05 AU, or are smaller than about 150 m in diameter, are not considered PHOs. This makes them a target for exploration. As of 2016, three near-Earth objects have been visited by spacecraft, more recently, a typical frame of reference for looking at NEOs has been through the scientific concept of risk. In this frame, the risk that any near-Earth object poses is typically seen through a lens that is a function of both the culture and the technology of human society, NEOs have been understood differently throughout history. Each time an NEO is observed, a different risk was posed and it is not just a matter of scientific knowledge. Such perception of risk is thus a product of religious belief, philosophic principles, scientific understanding, technological capabilities, and even economical resourcefulness.03 E −0.4 megatonnes. For instance, it gives the rate for bolides of 10 megatonnes or more as 1 per thousand years, however, the authors give a rather large uncertainty, due in part to uncertainties in determining the energies of the atmospheric impacts that they used in their determination

6.
Potentially hazardous object
–
A potentially hazardous object can be known not to be a threat to Earth for the next 100 years or more, if its orbit is reasonably well determined. Potentially hazardous asteroids with some threat of impacting Earth in the next 100 years are listed on the Sentry Risk Table, as of March 2017 there are 1,786 known potentially hazardous asteroids and only 205 have an observation arc shorter than 30 days. Of the known PHAs,157 are believed to be larger than one kilometer in diameter, a calculated diameter is only a rough estimate, as it is inferred from the objects varying brightness—observed and measured at various times—and the assumed, yet unknown reflectivity of its surface. Most of the discovered PHAs are Apollo asteroids and fewer belong to the group of Aten asteroids, after several astronomical surveys, the number of known PHAs has increased tenfold since the end of the 1990s. These surveys have led to a number of 15,802 discovered near-Earth objects. Most of them are asteroids, with just some 106 near-Earth comets, the Minor Planet Centers website Unusual Minor Planets also publishes detailed statistics for these objects. This is big enough to cause devastation to human settlements unprecedented in human history in the case of a land impact. Such impact events occur on average once per 10,000 years. NEOWISE data estimates that there are 4,700 ±1,500 potentially hazardous asteroids with a greater than 100 meters. As of 2012, an estimated 20 to 30 percent of these objects have been found, Asteroids larger than 35 meters across can pose a threat to a town or city. The diameter of most small asteroids is not well determined and can only be estimated based on their brightness, for this reason NASA and the Jet Propulsion Laboratory use the more practical measure of absolute magnitude. Any asteroid with a magnitude of 22. The NASA near-Earth object program uses an assumed albedo of 0.13 for this purpose, in May 2016, the asteroid size estimates arising from the Wide-field Infrared Survey Explorer and NEOWISE missions have been questioned, but the criticism has yet to undergo peer review. Several astronomical survey projects such as Lincoln Near-Earth Asteroid Research and Catalina Sky Survey continue to search for more PHOs, both professional and amateur astronomers participate in such monitoring. This is a reflection of the character of the Solar System. The two main scales used to categorize the impact hazards of asteroids are the Palermo Technical Impact Hazard Scale, the lowest numbered PHA is 1566 Icarus. The largest known Potentially hazardous asteroid is 1999 JM8 with a diameter of ~7 km, below is listed the largest PHA discovered in a given year. Historical data of the number of discovered PHA since 1999 are displayed in the bar charts—one for the total number

7.
Perihelion and aphelion
–
The perihelion is the point in the orbit of a celestial body where it is nearest to its orbital focus, generally a star. It is the opposite of aphelion, which is the point in the orbit where the body is farthest from its focus. The word perihelion stems from the Ancient Greek words peri, meaning around or surrounding, aphelion derives from the preposition apo, meaning away, off, apart. According to Keplers first law of motion, all planets, comets. Hence, a body has a closest and a farthest point from its parent object, that is, a perihelion. Each extreme is known as an apsis, orbital eccentricity measures the flatness of the orbit. Because of the distance at aphelion, only 93. 55% of the solar radiation from the Sun falls on a given area of land as does at perihelion. However, this fluctuation does not account for the seasons, as it is summer in the northern hemisphere when it is winter in the southern hemisphere and vice versa. Instead, seasons result from the tilt of Earths axis, which is 23.4 degrees away from perpendicular to the plane of Earths orbit around the sun. Winter falls on the hemisphere where sunlight strikes least directly, and summer falls where sunlight strikes most directly, in the northern hemisphere, summer occurs at the same time as aphelion. Despite this, there are larger land masses in the northern hemisphere, consequently, summers are 2.3 °C warmer in the northern hemisphere than in the southern hemisphere under similar conditions. Apsis Ellipse Solstice Dates and times of Earths perihelion and aphelion, 2000–2025 from the United States Naval Observatory

8.
Astronomical unit
–
The astronomical unit is a unit of length, roughly the distance from Earth to the Sun. However, that varies as Earth orbits the Sun, from a maximum to a minimum. Originally conceived as the average of Earths aphelion and perihelion, it is now defined as exactly 149597870700 metres, the astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a component in the definition of another unit of astronomical length. A variety of symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union used the symbol A for the astronomical unit, in 2006, the International Bureau of Weights and Measures recommended ua as the symbol for the unit. In 2012, the IAU, noting that various symbols are presently in use for the astronomical unit, in the 2014 revision of the SI Brochure, the BIPM used the unit symbol au. In ISO 80000-3, the symbol of the unit is ua. Earths orbit around the Sun is an ellipse, the semi-major axis of this ellipse is defined to be half of the straight line segment that joins the aphelion and perihelion. The centre of the sun lies on this line segment. In addition, it mapped out exactly the largest straight-line distance that Earth traverses over the course of a year, knowing Earths shift and a stars shift enabled the stars distance to be calculated. But all measurements are subject to some degree of error or uncertainty, improvements in precision have always been a key to improving astronomical understanding. Improving measurements were continually checked and cross-checked by means of our understanding of the laws of celestial mechanics, the expected positions and distances of objects at an established time are calculated from these laws, and assembled into a collection of data called an ephemeris. NASAs Jet Propulsion Laboratory provides one of several ephemeris computation services, in 1976, in order to establish a yet more precise measure for the astronomical unit, the IAU formally adopted a new definition. Equivalently, by definition, one AU is the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass. As with all measurements, these rely on measuring the time taken for photons to be reflected from an object. However, for precision the calculations require adjustment for such as the motions of the probe. In addition, the measurement of the time itself must be translated to a scale that accounts for relativistic time dilation

9.
Semi-major and semi-minor axes
–
In geometry, the major axis of an ellipse is its longest diameter, a line segment that runs through the center and both foci, with ends at the widest points of the perimeter. The semi-major axis is one half of the axis, and thus runs from the centre, through a focus. Essentially, it is the radius of an orbit at the two most distant points. For the special case of a circle, the axis is the radius. One can think of the axis as an ellipses long radius. The semi-major axis of a hyperbola is, depending on the convention, thus it is the distance from the center to either vertex of the hyperbola. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction. Thus a and b tend to infinity, a faster than b, the semi-minor axis is a line segment associated with most conic sections that is at right angles with the semi-major axis and has one end at the center of the conic section. It is one of the axes of symmetry for the curve, in an ellipse, the one, in a hyperbola. The semi-major axis is the value of the maximum and minimum distances r max and r min of the ellipse from a focus — that is. In astronomy these extreme points are called apsis, the semi-minor axis of an ellipse is the geometric mean of these distances, b = r max r min. The eccentricity of an ellipse is defined as e =1 − b 2 a 2 so r min = a, r max = a. Now consider the equation in polar coordinates, with one focus at the origin, the mean value of r = ℓ / and r = ℓ /, for θ = π and θ =0 is a = ℓ1 − e 2. In an ellipse, the axis is the geometric mean of the distance from the center to either focus. The semi-minor axis of an ellipse runs from the center of the ellipse to the edge of the ellipse, the semi-minor axis is half of the minor axis. The minor axis is the longest line segment perpendicular to the axis that connects two points on the ellipses edge. The semi-minor axis b is related to the axis a through the eccentricity e. A parabola can be obtained as the limit of a sequence of ellipses where one focus is fixed as the other is allowed to move arbitrarily far away in one direction

10.
Orbital eccentricity
–
The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is an orbit, values between 0 and 1 form an elliptical orbit,1 is a parabolic escape orbit. The term derives its name from the parameters of conic sections and it is normally used for the isolated two-body problem, but extensions exist for objects following a rosette orbit through the galaxy. In a two-body problem with inverse-square-law force, every orbit is a Kepler orbit, the eccentricity of this Kepler orbit is a non-negative number that defines its shape. The limit case between an ellipse and a hyperbola, when e equals 1, is parabola, radial trajectories are classified as elliptic, parabolic, or hyperbolic based on the energy of the orbit, not the eccentricity. Radial orbits have zero angular momentum and hence eccentricity equal to one, keeping the energy constant and reducing the angular momentum, elliptic, parabolic, and hyperbolic orbits each tend to the corresponding type of radial trajectory while e tends to 1. For a repulsive force only the trajectory, including the radial version, is applicable. For elliptical orbits, a simple proof shows that arcsin yields the projection angle of a circle to an ellipse of eccentricity e. For example, to view the eccentricity of the planet Mercury, next, tilt any circular object by that angle and the apparent ellipse projected to your eye will be of that same eccentricity. From Medieval Latin eccentricus, derived from Greek ἔκκεντρος ekkentros out of the center, from ἐκ- ek-, eccentric first appeared in English in 1551, with the definition a circle in which the earth, sun. Five years later, in 1556, a form of the word was added. The eccentricity of an orbit can be calculated from the state vectors as the magnitude of the eccentricity vector, e = | e | where. For elliptical orbits it can also be calculated from the periapsis and apoapsis since rp = a and ra = a, where a is the semimajor axis. E = r a − r p r a + r p =1 −2 r a r p +1 where, rp is the radius at periapsis. For Earths annual orbit path, ra/rp ratio = longest_radius / shortest_radius ≈1.034 relative to center point of path, the eccentricity of the Earths orbit is currently about 0.0167, the Earths orbit is nearly circular. Venus and Neptune have even lower eccentricity, over hundreds of thousands of years, the eccentricity of the Earths orbit varies from nearly 0.0034 to almost 0.058 as a result of gravitational attractions among the planets. The table lists the values for all planets and dwarf planets, Mercury has the greatest orbital eccentricity of any planet in the Solar System. Such eccentricity is sufficient for Mercury to receive twice as much solar irradiation at perihelion compared to aphelion, before its demotion from planet status in 2006, Pluto was considered to be the planet with the most eccentric orbit

11.
Mean anomaly
–
In celestial mechanics, the mean anomaly is an angle used in calculating the position of a body in an elliptical orbit in the classical two-body problem. Define T as the time required for a body to complete one orbit. In time T, the radius vector sweeps out 2π radians or 360°. The average rate of sweep, n, is then n =2 π T or n =360 ∘ T, define τ as the time at which the body is at the pericenter. From the above definitions, a new quantity, M, the mean anomaly can be defined M = n, because the rate of increase, n, is a constant average, the mean anomaly increases uniformly from 0 to 2π radians or 0° to 360° during each orbit. It is equal to 0 when the body is at the pericenter, π radians at the apocenter, if the mean anomaly is known at any given instant, it can be calculated at any later instant by simply adding n δt where δt represents the time difference. Mean anomaly does not measure an angle between any physical objects and it is simply a convenient uniform measure of how far around its orbit a body has progressed since pericenter. The mean anomaly is one of three parameters that define a position along an orbit, the other two being the eccentric anomaly and the true anomaly. Define l as the longitude, the angular distance of the body from the same reference direction. Thus mean anomaly is also M = l − ϖ, mean angular motion can also be expressed, n = μ a 3, where μ is a gravitational parameter which varies with the masses of the objects, and a is the semi-major axis of the orbit. Mean anomaly can then be expanded, M = μ a 3, and here mean anomaly represents uniform angular motion on a circle of radius a

12.
Degree (angle)
–
A degree, usually denoted by °, is a measurement of a plane angle, defined so that a full rotation is 360 degrees. It is not an SI unit, as the SI unit of measure is the radian. Because a full rotation equals 2π radians, one degree is equivalent to π/180 radians, the original motivation for choosing the degree as a unit of rotations and angles is unknown. One theory states that it is related to the fact that 360 is approximately the number of days in a year. Ancient astronomers noticed that the sun, which follows through the path over the course of the year. Some ancient calendars, such as the Persian calendar, used 360 days for a year, the use of a calendar with 360 days may be related to the use of sexagesimal numbers. The earliest trigonometry, used by the Babylonian astronomers and their Greek successors, was based on chords of a circle, a chord of length equal to the radius made a natural base quantity. One sixtieth of this, using their standard sexagesimal divisions, was a degree, Aristarchus of Samos and Hipparchus seem to have been among the first Greek scientists to exploit Babylonian astronomical knowledge and techniques systematically. Timocharis, Aristarchus, Aristillus, Archimedes, and Hipparchus were the first Greeks known to divide the circle in 360 degrees of 60 arc minutes, eratosthenes used a simpler sexagesimal system dividing a circle into 60 parts. Furthermore, it is divisible by every number from 1 to 10 except 7 and this property has many useful applications, such as dividing the world into 24 time zones, each of which is nominally 15° of longitude, to correlate with the established 24-hour day convention. Finally, it may be the case more than one of these factors has come into play. For many practical purposes, a degree is a small enough angle that whole degrees provide sufficient precision. When this is not the case, as in astronomy or for geographic coordinates, degree measurements may be written using decimal degrees, with the symbol behind the decimals. Alternatively, the sexagesimal unit subdivisions can be used. One degree is divided into 60 minutes, and one minute into 60 seconds, use of degrees-minutes-seconds is also called DMS notation. These subdivisions, also called the arcminute and arcsecond, are represented by a single and double prime. For example,40. 1875° = 40° 11′ 15″, or, using quotation mark characters, additional precision can be provided using decimals for the arcseconds component. The older system of thirds, fourths, etc. which continues the sexagesimal unit subdivision, was used by al-Kashi and other ancient astronomers, but is rarely used today

13.
Orbital inclination
–
Orbital inclination measures the tilt of an objects orbit around a celestial body. It is expressed as the angle between a plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth directly above the equator, the plane of the orbit is the same as the Earths equatorial plane. The general case is that the orbit is tilted, it spends half an orbit over the northern hemisphere. If the orbit swung between 20° north latitude and 20° south latitude, then its orbital inclination would be 20°, the inclination is one of the six orbital elements describing the shape and orientation of a celestial orbit. It is the angle between the plane and the plane of reference, normally stated in degrees. For a satellite orbiting a planet, the plane of reference is usually the plane containing the planets equator, for planets in the Solar System, the plane of reference is usually the ecliptic, the plane in which the Earth orbits the Sun. This reference plane is most practical for Earth-based observers, therefore, Earths inclination is, by definition, zero. Inclination could instead be measured with respect to another plane, such as the Suns equator or the invariable plane, the inclination of orbits of natural or artificial satellites is measured relative to the equatorial plane of the body they orbit, if they orbit sufficiently closely. The equatorial plane is the perpendicular to the axis of rotation of the central body. An inclination of 30° could also be described using an angle of 150°, the convention is that the normal orbit is prograde, an orbit in the same direction as the planet rotates. Inclinations greater than 90° describe retrograde orbits, thus, An inclination of 0° means the orbiting body has a prograde orbit in the planets equatorial plane. An inclination greater than 0° and less than 90° also describe prograde orbits, an inclination of 63. 4° is often called a critical inclination, when describing artificial satellites orbiting the Earth, because they have zero apogee drift. An inclination of exactly 90° is an orbit, in which the spacecraft passes over the north and south poles of the planet. An inclination greater than 90° and less than 180° is a retrograde orbit, an inclination of exactly 180° is a retrograde equatorial orbit. For gas giants, the orbits of moons tend to be aligned with the giant planets equator, the inclination of exoplanets or members of multiple stars is the angle of the plane of the orbit relative to the plane perpendicular to the line-of-sight from Earth to the object. An inclination of 0° is an orbit, meaning the plane of its orbit is parallel to the sky. An inclination of 90° is an orbit, meaning the plane of its orbit is perpendicular to the sky

14.
Longitude of the ascending node
–
The longitude of the ascending node is one of the orbital elements used to specify the orbit of an object in space. It is the angle from a direction, called the origin of longitude, to the direction of the ascending node. The ascending node is the point where the orbit of the passes through the plane of reference. Commonly used reference planes and origins of longitude include, For a geocentric orbit, Earths equatorial plane as the plane. In this case, the longitude is called the right ascension of the ascending node. The angle is measured eastwards from the First Point of Aries to the node, for a heliocentric orbit, the ecliptic as the reference plane, and the First Point of Aries as the origin of longitude. The angle is measured counterclockwise from the First Point of Aries to the node, the angle is measured eastwards from north to the node. pp.40,72,137, chap. In the case of a star known only from visual observations, it is not possible to tell which node is ascending. In this case the orbital parameter which is recorded is the longitude of the node, Ω, here, n=<nx, ny, nz> is a vector pointing towards the ascending node. The reference plane is assumed to be the xy-plane, and the origin of longitude is taken to be the positive x-axis, K is the unit vector, which is the normal vector to the xy reference plane. For non-inclined orbits, Ω is undefined, for computation it is then, by convention, set equal to zero, that is, the ascending node is placed in the reference direction, which is equivalent to letting n point towards the positive x-axis. Kepler orbits Equinox Orbital node perturbation of the plane can cause revolution of the ascending node

15.
Argument of periapsis
–
The argument of periapsis, symbolized as ω, is one of the orbital elements of an orbiting body. Parametrically, ω is the angle from the ascending node to its periapsis. For specific types of orbits, words such as perihelion, perigee, periastron, an argument of periapsis of 0° means that the orbiting body will be at its closest approach to the central body at the same moment that it crosses the plane of reference from South to North. An argument of periapsis of 90° means that the body will reach periapsis at its northmost distance from the plane of reference. Adding the argument of periapsis to the longitude of the ascending node gives the longitude of the periapsis, however, especially in discussions of binary stars and exoplanets, the terms longitude of periapsis or longitude of periastron are often used synonymously with argument of periapsis. In the case of equatorial orbits, the argument is strictly undefined, where, ex and ey are the x- and y-components of the eccentricity vector e. In the case of circular orbits it is assumed that the periapsis is placed at the ascending node. Kepler orbit Orbital mechanics Orbital node

16.
Minimum orbit intersection distance
–
Minimum orbit intersection distance is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the orbits of two bodies. Of greatest interest is the risk of a collision with Earth, Earth MOID is often listed on comet and asteroid databases such as the JPL Small-Body Database. MOID values are defined with respect to other bodies as well, Jupiter MOID, Venus MOID. An object is classified as a hazardous object – that is, posing a possible risk to Earth – if, among other conditions. A low MOID does not mean that a collision is inevitable as the planets frequently perturb the orbit of small bodies. It is also necessary that the two bodies reach that point in their orbits at the time before the smaller body is perturbed into a different orbit with a different MOID value. Two Objects gravitationally locked in orbital resonance may never approach one another, numerical integrations become increasingly divergent as trajectories are projected further forward in time, especially beyond times where the smaller body is repeatedly perturbed by other planets. MOID has the convenience that it is obtained directly from the elements of the body. The only object that has ever been rated at 4 on the Torino Scale and this is not the smallest Earth MOID in the catalogues, many bodies with a small Earth MOID are not classed as PHOs because the objects are less than roughly 140 meters in diameter. Earth MOID values are more practical for asteroids less than 140 meters in diameter as those asteroids are very dim. It is even smaller at the more precise JPL Small Body Database

17.
Lunar distance (astronomy)
–
Lunar distance is as a unit of measure in astronomy. It is the distance from the center of Earth to the center of the Moon. More technically, it is the mean semi-major axis of the lunar orbit. It may also refer to the distance between the centers of the Earth and the Moon, or less commonly, the instantaneous Earth-Moon distance. The lunar distance is approximately a quarter of a million miles, Lunar distance is also called Earth-Moon distance, Earth–Moon characteristic distance, or distance to the Moon, and commonly indicated with LD or Δ ⊕ L. The mean semi-major axis has a value of 384,402 km, the time-averaged distance between Earth and Moon centers is 385,000.6 km. The actual distance varies over the course of the orbit of the Moon, from 356,500 km at the perigee to 406,700 km at apogee, Lunar distance is commonly used to express the distance to near-Earth object encounters. The measurement is useful in characterizing the lunar radius, the mass of the Sun. Millimeter-precision measurements of the distance are made by measuring the time taken for light to travel between LIDAR stations on the Earth and retroreflectors placed on the Moon. The Moon is spiraling away from the Earth at a rate of 3.8 cm per year. By coincidence, the diameter of corner cubes in retroreflectors on the Moon is also 3.8 cm, the instantaneous lunar distance is constantly changing. In fact the distance between the Moon and Earth can change by as much as 75 m/s, or more than 1,000 kilometers in just 6 hours. There are other effects that influence the lunar distance. Some factors are described in this section, the distance to the Moon can be measured to an accuracy of 2 mm over a 1-hour sampling period, which results in an overall uncertainty of 2–3 cm for the average distance. However, due to its orbit with varying eccentricity, the instantaneous distance varies with monthly periodicity. Furthermore, the distance is perturbed by the effects of various astronomical bodies - most significantly the Sun. Other forces responsible for minuscule perturbations are other planets in the system, asteroids, tidal forces. The effect of pressure from the sun contributes an amount of ±3.6 mm to the lunar distance

18.
Solar System
–
The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets, of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the collapse of a giant interstellar molecular cloud. The vast majority of the mass is in the Sun. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being composed of rock. The four outer planets are giant planets, being more massive than the terrestrials. All planets have almost circular orbits that lie within a flat disc called the ecliptic. The Solar System also contains smaller objects, the asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptunes orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets, identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds. Six of the planets, at least four of the dwarf planets, each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, the heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium, it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, the Solar System is located in the Orion Arm,26,000 light-years from the center of the Milky Way. For most of history, humanity did not recognize or understand the concept of the Solar System, the invention of the telescope led to the discovery of further planets and moons. The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99. 86% of the known mass. The Suns four largest orbiting bodies, the giant planets, account for 99% of the mass, with Jupiter. The remaining objects of the Solar System together comprise less than 0. 002% of the Solar Systems total mass, most large objects in orbit around the Sun lie near the plane of Earths orbit, known as the ecliptic

19.
4 Vesta
–
Vesta, minor-planet designation 4 Vesta, is one of the largest objects in the asteroid belt, with a mean diameter of 525 kilometres. It was discovered by the German astronomer Heinrich Wilhelm Olbers on 29 March 1807 and is named after Vesta, Vesta is the second-most-massive and second-largest body in the asteroid belt after the dwarf planet Ceres, and it contributes an estimated 9% of the mass of the asteroid belt. It is slightly larger than Pallas, though more massive. Vesta is the last remaining rocky protoplanet of the kind that formed the terrestrial planets, numerous fragments of Vesta were ejected by collisions one and two billion years ago that left two enormous craters occupying much of Vestas southern hemisphere. Debris from these events has fallen to Earth as howardite–eucrite–diogenite meteorites, Vesta is the brightest asteroid visible from Earth. Its maximum distance from the Sun is slightly greater than the distance of Ceres from the Sun. NASAs Dawn spacecraft entered orbit around Vesta on 16 July 2011 for an exploration and left orbit on 5 September 2012 en route to its final destination. Researchers continue to examine data collected by Dawn for additional insights into the formation, Heinrich Olbers discovered Pallas in 1802, the year after the discovery of Ceres. He proposed that the two objects were the remnants of a destroyed planet and these orbital intersections were located in the constellations of Cetus and Virgo. Olbers commenced his search in 1802, and on 29 March 1807 he discovered Vesta in the constellation Virgo—a coincidence, because Ceres, Pallas, and Vesta are not fragments of a larger body. Because the asteroid Juno had been discovered in 1804, this made Vesta the fourth object to be identified in the region that is now known as the asteroid belt, the discovery was announced in a letter addressed to German astronomer Johann H. Schröter dated 31 March. Gauss decided on the Roman virgin goddess of home and hearth, Vesta was the fourth asteroid to be discovered, hence the number 4 in its formal designation. The name Vesta, or national variants thereof, is in use with two exceptions, Greece and China. In Greek, the name adopted was the Hellenic equivalent of Vesta, Hestia, in English, in Chinese, Vesta is called the hearth-god star, 灶神星 zàoshénxīng, in contrast to the goddess Vesta, who goes by her Latin name. Upon its discovery, Vesta was, like Ceres, Pallas, the symbol representing the altar of Vesta with its sacred fire and was designed by Gauss. In Gausss conception, this was drawn, in its modern form, after the discovery of Vesta, no further objects were discovered for 38 years, and the Solar System was thought to have eleven planets. However, in 1845, new asteroids started being discovered at a rapid pace and it soon became clear that it would be impractical to continue inventing new planetary symbols indefinitely, and some of the existing ones proved difficult to draw quickly. That year, the problem was addressed by Benjamin Apthorp Gould, who suggested numbering asteroids in their order of discovery, thus, the fourth asteroid, Vesta, acquired the generic symbol ④

20.
Burj Khalifa
–
The Burj Khalifa, known as the Burj Dubai before its inauguration, is a megatall skyscraper in Dubai, United Arab Emirates. It has a height of 828 m, and with its antenna included, it stands a total height of 829.8 m, making it the tallest building. Construction of the Burj Khalifa began in 2004, with the exterior completed 5 years later in 2009, the primary structure is reinforced concrete. The building was opened in 2010 as part of a new development called Downtown Dubai and it is designed to be the centrepiece of large-scale, mixed-use development. The decision to build the building is based on the governments decision to diversify from an oil-based economy. The building was named in honour of the ruler of Abu Dhabi and president of the United Arab Emirates, Khalifa bin Zayed Al Nahyan, Abu Dhabi, the building broke numerous height records, including its designation as the tallest tower in the world. Burj Khalifa was designed by Adrian Smith, then of Skidmore, Owings & Merrill, whose firm designed the Willis Tower, Hyder Consulting was chosen to be the supervising engineer with NORR Group Consultants International Limited chosen to supervise the architecture of the project. The design is derived from the Islamic architecture of the region, the Y-shaped tripartite floor geometry is designed to optimize residential and hotel space. A buttressed central core and wings are used to support the height of the building, although this design was derived from Tower Palace III, the Burj Khalifa’s central core houses all vertical transportation with the exception of egress stairs within each of the wings. The structure also features a system which is designed to withstand Dubais hot summer temperatures. It contains a total of 57 elevators and 8 escalators, critical reception to Burj Khalifa has been generally positive, and the building has received many awards. However, the issues during construction were controversial, since the building was built primarily by migrant workers from South Asia with several allegations of mistreatment. Poor working conditions are common, as the result of the lack of minimum wage laws in the United Arab Emirates, several instances of suicides have been reported, which is not uncommon for migrant construction workers in Dubai despite safety precautions in place. Construction began on 6 January 2004, with the exterior of the completed on 1 October 2009. The building officially opened on 4 January 2010, and is part of the new 2 km2 development called Downtown Dubai at the First Interchange along Sheikh Zayed Road, near Dubais main business district. The towers architecture and engineering were performed by Skidmore, Owings and Merrill of Chicago, with Adrian Smith as chief architect, the primary contractor was Samsung C&T of South Korea. The towers construction was done by the division of Al Ghurair Investment group. The decision to build Burj Khalifa is reportedly based on the decision to diversify from an oil-based economy to one that is service

21.
Sentry (monitoring system)
–
Whenever a potential impact is detected it will be analyzed and the results immediately published on the Near Earth Object Program. However, several weeks of data are not enough to conclusively identify an impact years in the future. By contrast, eliminating an entry on the page is a negative prediction. Scientists warn against worrying about the possibility of impact with a based on only a few weeks of optical data that show a possible Earth encounter years from now. The Impact Risk page lists a number of lost objects that are, for all purposes, permanent residents of the risk page. 1997 XR2 was serendipitously rediscovered in 2006 after being lost for more than 8 years, some objects on the Sentry Risk Table, such as 2000 SG344, might even be man-made. Notable objects currently on the risk page include,1950 DA,99942 Apophis,101955 Bennu,2009 FD,1994 WR12, and 2010 RF12. Notable asteroids removed from Sentry in the last few years include,2007 VK184,2013 BP73,2008 CK70,2013 TV135,2011 BT15,367943 Duende, and 2011 AG5. The diameter of most near-Earth asteroids that have not been studied by radar or infrared can generally only be estimated within about a factor of 2 based on the absolute magnitude. Their mass, consequently, is uncertain by about a factor of 10, for near-Earth asteroids without a well-determined diameter, Sentry assumes a generic albedo of 0.15. More than two dozen known asteroids have higher than a one in a chance of impacting into Earth within the next 100 years. In August 2013, the Sentry Risk Table started using planetary ephemeris for all NEO orbit determinations, dE431 better models the gravitational perturbations of the planets and includes the 16 most massive main-belt asteroids. JPL launched major changes to the website in February 2017, as of February 2017 there are roughly 680 near-Earth asteroids listed on the risk table and roughly 2000 asteroids have been removed from the risk table since it launched in 2002

22.
Universal Time
–
Universal Time is a time standard based on Earths rotation. It is a continuation of Greenwich Mean Time, i. e. the mean solar time on the Prime Meridian at Greenwich, London. In fact, the expression Universal Time is ambiguous, as there are versions of it. All of these versions of UT, except for UTC, are based on Earths rotation relative to distant celestial objects, UTC is based on International Atomic Time, with leap seconds added to keep it within 0.9 second of UT1. Prior to the introduction of time, each municipality throughout the civilized world set its official clock, if it had one. Greenwich Mean Time, where all clocks in Britain were set to the time, was established to solve this problem. Chronometers or telegraphy were used to synchronize these clocks, Standard time, as originally proposed by Scottish-Canadian Sir Sandford Fleming in 1879, divided the world into twenty-four time zones, each one covering 15 degrees of longitude. All clocks within each zone would be set to the time as the others. This location was chosen because by 1884 two-thirds of all nautical charts, the conference did not adopt Flemings time zones because they were outside the purpose for which it was called, which was to choose a basis for universal time. During the period between 1848 and 1972, all of the countries adopted time zones based on the Greenwich meridian. The term Greenwich Mean Time persists, however, in usage to this day in reference to civil timekeeping. Based on the rotation of the Earth, time can be measured by observing celestial bodies crossing the meridian every day. Astronomers found that it was accurate to establish time by observing stars as they crossed a meridian rather than by observing the position of the Sun in the sky. Nowadays, UT in relation to International Atomic Time is determined by Very Long Baseline Interferometry observations of distant quasars, the rotation of the Earth and UT are monitored by the International Earth Rotation and Reference Systems Service. The International Astronomical Union also is involved in setting standards, the rotation of the Earth is somewhat irregular, and is very gradually slowing due to tidal acceleration. Furthermore, the length of the second was determined from observations of the Moon between 1750 and 1890. All of these cause the mean solar day, on the average, to be slightly longer than the nominal 86,400 SI seconds. As UT is slightly irregular in its rate, astronomers introduced Ephemeris Time, thus, civil broadcast standards for time and frequency usually follow International Atomic Time closely, but occasionally step in order to prevent them from drifting too far from mean solar time

23.
Goldstone Deep Space Communications Complex
–
The Goldstone Deep Space Communications Complex, commonly called the Goldstone Observatory, is located in the Mojave Desert near Barstow in the U. S. state of California. Operated by the US National Aeronautics and Space Administrations Jet Propulsion Laboratory, its purpose is to track. It is named after Goldstone, California, a nearby gold-mining ghost town, the complex includes the Pioneer Deep Space Station, which is a U. S. National Historic Landmark. The current communications complex is one of three in the NASA Deep Space Network, the others being the Madrid Deep Space Communications Complex and the Canberra Deep Space Communication Complex. Five large parabolic antennas are located at the Goldstone site to handle the workload, the antennas function similarly to a home satellite dish. The radio frequencies used for communication are in the microwave part of the radio spectrum, S band, X band. In addition to receiving radio signals from the spacecraft, the antennas transmit commands to the spacecraft with high power radio transmitters powered by klystron tubes. A major goal in the design of the station is to reduce interference with the weak incoming downlink radio signals by natural, the remote Mojave Desert location was chosen because it is far from manmade sources of radio noise such as motor vehicles. The RF front ends of the receivers at the dishes use ruby masers. It is commonly believed that the first American satellite, Explorer 1, was confirmed to be in orbit by the use of the phrase Goldstone has the bird. However, Goldstone was not in operation at the time of Explorer 1, others claim that the actual phrase was Gold has it. Incorrectly identifying Gold as a tracking station at Earthquake Valley, east of Julian. In fact, Gold Station was located at the Air Force Missile Test Center in Florida, the Goldstone Deep Space Communications Complex conducts tours of its facility and museum to middle and high schools, as well as individuals interested in visiting. The DSS14, Mars telescope is specifically quoted in the webcomic Wondermark, episode 881 In which a Standard is Questioned

24.
Apparent magnitude
–
The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value, the Sun, at apparent magnitude of −27, is the brightest object in the sky. It is adjusted to the value it would have in the absence of the atmosphere, furthermore, the magnitude scale is logarithmic, a difference of one in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry, apparent magnitudes are used to quantify the brightness of sources at ultraviolet, visible, and infrared wavelengths. An apparent magnitude is measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V filter band would be denoted either as mV or often simply as V, the scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the sky were said to be of first magnitude, whereas the faintest were of sixth magnitude. Each grade of magnitude was considered twice the brightness of the following grade and this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest, and is generally believed to have originated with Hipparchus. This implies that a star of magnitude m is 2.512 times as bright as a star of magnitude m +1 and this figure, the fifth root of 100, became known as Pogsons Ratio. The zero point of Pogsons scale was defined by assigning Polaris a magnitude of exactly 2. However, with the advent of infrared astronomy it was revealed that Vegas radiation includes an Infrared excess presumably due to a disk consisting of dust at warm temperatures. At shorter wavelengths, there is negligible emission from dust at these temperatures, however, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the scale was extrapolated to all wavelengths on the basis of the black body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance for the zero magnitude point, with the modern magnitude systems, brightness over a very wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30, astronomers have developed other photometric zeropoint systems as alternatives to the Vega system. The AB magnitude zeropoint is defined such that an objects AB, the dimmer an object appears, the higher the numerical value given to its apparent magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor 5√100 ≈2.512. Inverting the above formula, a magnitude difference m1 − m2 = Δm implies a brightness factor of F2 F1 =100 Δ m 5 =100.4 Δ m ≈2.512 Δ m

25.
Elongation (astronomy)
–
In astronomy, a planets elongation is the angle between the Sun and the planet, with Earth as the reference point. The greatest elongation of a given planet occurs when this inner planet’s position, when a planet is at its greatest elongation, it is farthest from the Sun as viewed from Earth, so its view is also best at that point. When an inferior planet is visible after sunset, it is near its greatest eastern elongation, when an inferior planet is visible before sunrise, it is near its greatest western elongation. The value of the greatest elongation, for Mercury, is between 18° and 28°, and for Venus between 45° and 47° and this value varies because the orbits of the planets are elliptical, rather than perfect circles. Another minor contributor to this inconsistency is orbital inclination, each orbit is in a slightly different plane. Refer to astronomical tables and websites such as heavens-above to see when the planets reach their next maximum elongations, greatest elongations of a planet happen periodically, with a greatest eastern elongation followed by a greatest western elongation, and vice versa. The period depends on the angular velocity of Earth and the planet. The time it takes to complete this period is the period of the planet. Let T be the period, ω be the angular velocity, ωe Earths angular velocity. For example, Venuss year is 225 days, and Earths is 365 days, thus Venuss synodic period, which gives the time between two subsequent eastern greatest elongations, is 584 days. These values are approximate, because the planets do not have circular, coplanar orbits. Superior planets, dwarf planets and asteroids undergo a different cycle, in other words, as seen from an observer on the superior planet at opposition, the Earth appears at inferior conjunction with the Sun. Technically, the moment of opposition is slightly different from the moment of maximum elongation. For example, Pluto, whose orbit is inclined to the Earths orbital plane. All superior planets are most easily visible at their oppositions because they are near their closest approach to Earth and are also above the horizon all night, the variation in magnitude caused by changes in elongation are greater the closer the planets orbit is to the Earths. As one moves out, the difference in magnitude caused by the difference in elongation gradually fall. Since asteroids travel in a not much larger than the Earths. Sometimes elongation may instead refer to the distance of a moon of another planet from its central planet

26.
Jet Propulsion Laboratory
–
The Jet Propulsion Laboratory is a federally funded research and development center and NASA field center in La Cañada Flintridge, California and Pasadena, California, United States. The JPL is managed by the nearby California Institute of Technology for NASA, the laboratorys primary function is the construction and operation of planetary robotic spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASAs Deep Space Network and they are also responsible for managing the JPL Small-Body Database, and provides physical data and lists of publications for all known small Solar System bodies. The JPLs Space Flight Operations Facility and Twenty-Five-Foot Space Simulator are designated National Historic Landmarks, JPL traces its beginnings to 1936 in the Guggenheim Aeronautical Laboratory at the California Institute of Technology when the first set of rocket experiments were carried out in the Arroyo Seco. Malinas thesis advisor was engineer/aerodynamicist Theodore von Kármán, who arranged for U. S. Army financial support for this GALCIT Rocket Project in 1939. In 1941, Malina, Parsons, Forman, Martin Summerfield, in 1943, von Kármán, Malina, Parsons, and Forman established the Aerojet Corporation to manufacture JATO motors. The project took on the name Jet Propulsion Laboratory in November 1943, during JPLs Army years, the laboratory developed two deployed weapon systems, the MGM-5 Corporal and MGM-29 Sergeant intermediate range ballistic missiles. These missiles were the first US ballistic missiles developed at JPL and it also developed a number of other weapons system prototypes, such as the Loki anti-aircraft missile system, and the forerunner of the Aerobee sounding rocket. At various times, it carried out testing at the White Sands Proving Ground, Edwards Air Force Base. A lunar lander was developed in 1938-39 which influenced design of the Apollo Lunar Module in the 1960s. The team lost that proposal to Project Vanguard, and instead embarked on a project to demonstrate ablative re-entry technology using a Jupiter-C rocket. They carried out three successful flights in 1956 and 1957. Using a spare Juno I, the two organizations then launched the United States first satellite, Explorer 1, on February 1,1958, JPL was transferred to NASA in December 1958, becoming the agencys primary planetary spacecraft center. JPL engineers designed and operated Ranger and Surveyor missions to the Moon that prepared the way for Apollo, JPL also led the way in interplanetary exploration with the Mariner missions to Venus, Mars, and Mercury. In 1998, JPL opened the Near-Earth Object Program Office for NASA, as of 2013, it has found 95% of asteroids that are a kilometer or more in diameter that cross Earths orbit. JPL was early to employ women mathematicians, in the 1940s and 1950s, using mechanical calculators, women in an all-female computations group performed trajectory calculations. In 1961, JPL hired Dana Ulery as their first woman engineer to work alongside male engineers as part of the Ranger and Mariner mission tracking teams, when founded, JPLs site was a rocky flood-plain just outside the city limits of Pasadena. Almost all of the 177 acres of the U. S, the city of La Cañada Flintridge, California was incorporated in 1976, well after JPL attained international recognition with a Pasadena address

27.
Wayback Machine
–
The Internet Archive launched the Wayback Machine in October 2001. It was set up by Brewster Kahle and Bruce Gilliat, and is maintained with content from Alexa Internet, the service enables users to see archived versions of web pages across time, which the archive calls a three dimensional index. Since 1996, the Wayback Machine has been archiving cached pages of websites onto its large cluster of Linux nodes and it revisits sites every few weeks or months and archives a new version. Sites can also be captured on the fly by visitors who enter the sites URL into a search box, the intent is to capture and archive content that otherwise would be lost whenever a site is changed or closed down. The overall vision of the machines creators is to archive the entire Internet, the name Wayback Machine was chosen as a reference to the WABAC machine, a time-traveling device used by the characters Mr. Peabody and Sherman in The Rocky and Bullwinkle Show, an animated cartoon. These crawlers also respect the robots exclusion standard for websites whose owners opt for them not to appear in search results or be cached, to overcome inconsistencies in partially cached websites, Archive-It. Information had been kept on digital tape for five years, with Kahle occasionally allowing researchers, when the archive reached its fifth anniversary, it was unveiled and opened to the public in a ceremony at the University of California, Berkeley. Snapshots usually become more than six months after they are archived or, in some cases, even later. The frequency of snapshots is variable, so not all tracked website updates are recorded, Sometimes there are intervals of several weeks or years between snapshots. After August 2008 sites had to be listed on the Open Directory in order to be included. As of 2009, the Wayback Machine contained approximately three petabytes of data and was growing at a rate of 100 terabytes each month, the growth rate reported in 2003 was 12 terabytes/month, the data is stored on PetaBox rack systems manufactured by Capricorn Technologies. In 2009, the Internet Archive migrated its customized storage architecture to Sun Open Storage, in 2011 a new, improved version of the Wayback Machine, with an updated interface and fresher index of archived content, was made available for public testing. The index driving the classic Wayback Machine only has a bit of material past 2008. In January 2013, the company announced a ground-breaking milestone of 240 billion URLs, in October 2013, the company announced the Save a Page feature which allows any Internet user to archive the contents of a URL. This became a threat of abuse by the service for hosting malicious binaries, as of December 2014, the Wayback Machine contained almost nine petabytes of data and was growing at a rate of about 20 terabytes each week. Between October 2013 and March 2015 the websites global Alexa rank changed from 162 to 208, in a 2009 case, Netbula, LLC v. Chordiant Software Inc. defendant Chordiant filed a motion to compel Netbula to disable the robots. Netbula objected to the motion on the ground that defendants were asking to alter Netbulas website, in an October 2004 case, Telewizja Polska USA, Inc. v. Echostar Satellite, No.02 C3293,65 Fed. 673, a litigant attempted to use the Wayback Machine archives as a source of admissible evidence, Telewizja Polska is the provider of TVP Polonia and EchoStar operates the Dish Network

28.
NEODyS
–
NEODyS is an Italian and Spanish service that provides information on Near Earth Objects with a convenient Web-based interface. It is based on a continually and automatically maintained database of near earth asteroid orbits and this site provides a number of services to the NEO community. The main service is a monitoring system of all near-Earth asteroids covering a period until the year 2100. Risk Page, The most important service is the production of a Risk Page where all NEOs with probabilities of hitting the Earth greater of 10−11 from now until 2100 are shown in a Risk list. Each object has its own Impactor Table which shows many parameters useful to determine the risk assessment, observation prediction, It provides the position of the object at a specific time, information useful for the observer and a graph showing the uncertainty on sky. Orbital Information, It provides the dynamical parameters of the orbit of the object, MOID, It shows the analysis of the Minimum Orbital Intersection Distance of the object. Proper elements, It shows the properties of the object. Observational Information, It provides data of both optical and radar observations and their statistical performance, close approaches, It provides a table with all the close approaches until 2100 with the planets of the Solar System. Search, It provides the possibility of queries in the according to the orbital parameters or the observational conditions or the close approaches with the planets of the Solar System. Observatories, It is possible to access the information regarding observatories, the database of orbits is continually and automatically maintained with the most recent Minor Planet Center observations. The orbits are computed with the OrbFit software package provided by the OrbFit Consortium, all of the computational services provided by this site can also be done with this software package. NEODyS is continually expanding and improving, the followings are the next tasks of the project, Uncertainties of all the quantities provided with the orbit, e. g. A new web-interface is available running the free software PHP and this allows a more flexible and easy to update system. In the same period the system switched to the new version of the Fortran 95 code OrbFit 4.0, the NEODyS team is composed by Andrea Milani, Maria Eugenia Sansaturio, Oscar Arratia, Fabrizio Bernardi, Giovanni F. Gronchi, Giovanni B. NeoDys official website, and the Spanish duplicate system Orbfit NASA JPL Near-Earth Object Program E. A. R. N

29.
Small Solar System body
–
A Small Solar System Body is an object in the Solar System that is neither a planet, nor a dwarf planet, nor a natural satellite. The term was first defined in 2006 by the International Astronomical Union, all other objects, except satellites, orbiting the Sun shall be referred to collectively as Small Solar System Bodies. These currently include most of the Solar System asteroids, most Trans-Neptunian Objects, comets and this encompasses all comets and all minor planets other than those that are dwarf planets. Except for the largest, which are in equilibrium, natural satellites differ from small Solar System bodies not in size. The orbits of satellites are not centered on the Sun, but around other Solar System objects such as planets, dwarf planets. Some of the larger small Solar System bodies may be reclassified in future as dwarf planets, the orbits of the vast majority of small Solar System bodies are located in two distinct areas, namely the asteroid belt and the Kuiper belt. These two belts possess some internal structure related to perturbations by the planets, and have fairly loosely defined boundaries. Other areas of the Solar System also encompass small bodies in smaller concentrations and these include the near-Earth asteroids, centaurs, comets, and scattered disc objects

30.
Minor-planet moon
–
A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. It is thought that many asteroids and Kuiper belt objects may possess moons, the first modern era mention of the possibility of an asteroid satellite was in connection with an occultation of the bright star Gamma Ceti by the minor planet Hebe in 1977. The observer, amateur astronomer Paul D. Maley, detected an unmistakable 0.5 second disappearance of this naked eye star from a site near Victoria, many hours later, several observations were reported in Mexico attributed to the occultation by Hebe itself. Although not confirmed this documents the first formally documented case of a companion of an asteroid. As of October 2016, there are over 300 minor planets known to have moons, in addition to the terms satellite and moon, the term binary is sometimes used for minor planets with moons, and triple for minor planets with two moons. If one object is much bigger it can be referred to as the primary, when binary minor planets are similar in size, the Minor Planet Center refers to them as binary companions instead of referring to the smaller body as a satellite. A good example of a true binary is the 90 Antiope system, small satellites are often referred to as moonlets. As of February 2017, over 330 moons of planets have been discovered. For example, in 1978, stellar occultation observations were claimed as evidence of a satellite for the asteroid 532 Herculina, however, later more-detailed imaging by the Hubble Telescope did not reveal a satellite, and the current consensus is that Herculina does not have a significant satellite. There were other reports of asteroids having companions in the following years. In 1993, the first asteroid moon was confirmed when the Galileo probe discovered the small Dactyl orbiting 243 Ida in the asteroid belt, the second was discovered around 45 Eugenia in 1998. In 2001,617 Patroclus and its same-sized companion Menoetius became the first known asteroids in the Jupiter trojans. The first trans-Neptunian binary after Pluto–Charon,1998 WW31, was resolved in 2002. Triple asteroids, or trinary asteroids, are known since 2005 and this was followed by the discovery of a second moon orbiting 45 Eugenia. Also in 2005, the Kuiper belt object Haumea was discovered to have two moons, making it the second KBO after Pluto known to have more than one moon, additionally,216 Kleopatra and 93 Minerva were discovered to be trinary asteroids in 2008 and 2009 respectively. Since the first few trinary asteroids were discovered, more continue to be discovered at a rate of one a year. Most recently discovered was a moon orbiting the belt asteroid 130 Elektra. List of multiple planets, The data about the populations of binary objects are still patchy

The asteroid belt is the circumstellar disc in the Solar System located roughly between the orbits of the planets Mars …

By far the largest object within the belt is Ceres. The total mass of the asteroid belt is significantly less than Pluto's, and approximately twice that of Pluto's moon Charon.

Johannes Kepler, who first noticed in 1596 that there was something strange about the orbits of Mars and Jupiter.

Giuseppe Piazzi, discoverer of Ceres, the largest object in the asteroid belt. For several decades after its discovery Ceres was known as a planet, after which it was reclassified as asteroid. In 2006, it was designated as a dwarf planet.

951 Gaspra, the first asteroid imaged by a spacecraft, as viewed during Galileos 1991 flyby; colors are exaggerated

This graphic shows the distance from the Oort cloud to the rest of the Solar System and two of the nearest stars measured in astronomical units. The scale is logarithmic, with each specified distance ten times further out than the previous one. Red arrow indicates location of Voyager 1, a space probe that will reach the Oort cloud in 300 years.

Simulation showing Outer Planets and Kuiper Belt: a) Before Jupiter/Saturn 2:1 resonance b) Scattering of Kuiper-belt objects into the Solar System after the orbital shift of Neptune c) After ejection of Kuiper-belt bodies by Jupiter

The infrared spectra of both Eris and Pluto, highlighting their common methane absorption lines

The astronomical unit (symbol: au or ua) is a unit of length, roughly the distance from Earth to the Sun. However, that …

The red line indicates the Earth–Sun distance, which on average is about 1 astronomical unit.

Transits of Venus across the face of the Sun were, for a long time, the best method of measuring the astronomical unit, despite the difficulties (here, the so-called "black drop effect") and the rarity of observations.

The astronomical unit is used as the baseline of the triangle to measure stellar parallaxes (distances in the image are not to scale).

In statistics, the 68–95–99.7 rule is a shorthand used to remember the percentage of values that lie within a band …

For the normal distribution, the values within one standard deviation of the mean account for 68.27% of the set; while within two standard deviations account for 95.45%; and within three standard deviations account for 99.73%.

Prediction interval (on the y-axis) given from the standard score (on the x-axis). The y-axis is logarithmically scaled (but the values on it are not modified).

In celestial mechanics, the mean anomaly is an angle used in calculating the position of a body in an elliptical orbit …

Area swept out per unit time by an object in an elliptical orbit (grey) and by an imaginary object in a circular orbit (red) which completes its orbit in the same period of time. Both sweep out equal areas in equal times, but the angular rate of sweep varies for the elliptical orbit and is constant for the circular orbit. Shown are mean anomaly and true anomaly for two units of time.